1. Field of the Invention
This invention relates to a locking differential for use with motor vehicles, and is more particularly concerned with an improvement in a locking differential wherein friction torque producible by friction disks can easily be varied.
2. Description of the Related Art
A conventional pre-load type locking differential includes a multi-plate clutch having a plurality of friction disks to produce friction torque. A widely used pre-load type locking differential is disclosed in Japanese utility model laid open publication No. Sho 57/130039. The disclosed locking differential includes a differential case within which differential side gears are arranged in confronting relation. A spring assembly for pre-load is interposed between the inner ends of the side gears to enable the multi-plate clutch to produce friction torque.
With reference particularly to FIGS. 4 through 7, a differential case 1 has sleeve portions 1a, 1a, both of which are rotatably mounted on a differential carrier (not shown) by a suitable bearing assembly. As is well known in the art, a ring gear (not shown) is fixedly mounted on the differential case 1. With this arrangement, torque is transmitted through the ring gear to the differential case 1 to rotate the same about the common central axis of the sleeve portions 1a, 1a. Within the differential case 1, a pair of differential side gears 2, 2 mesh with a corresponding pair of pinion gears (or four pinion gears) 3, 3. Right and left axle shafts (not shown) are inserted into the sleeve portions 1a, 1a to join the differential side gears 2, 2, for example, by serration.
The pinion gears 3, 3 are rotatably mounted on the pinion shaft 4, both ends of which are freely journalled in the differential case 1. The pinion shaft 4 has a retainer ring 5 at its center. Interposed between both sides of the retainer ring 5 and the inner ends of the side gears 2, 2 are disks 6, 6 for supporting a spring assembly. One of the disks 6, 6 has an integral sleeve and the other disk has a central shaft. Upon connection of the sleeve and the central shaft of the disks 6, 6, the disks are relatively movable in a lateral direction in FIG. 4, and are rotatable together. One of the disks (left-hand disk in FIG. 4) is rendered nonrotatable relative to the retainer ring 5 under the influence of a pin 15. A large diameter pre-load spring 7 and a small diameter pre-load spring 8 are positioned in the retainer ring 5 to urge the side gears 2, 2 through the disks 6, 6. As a result, the side gears 2, 2 can be moved axially outwardly. As noted above, the differential may include four pinion gears. In this case, a pinion shaft takes the form of a cross.
Multi-plate clutches 9, 9 are interposed between the rear surfaces of the side gears 2, 2 and the inner surfaces of the differential case 1, respectively. As is best seen in FIG. 5, each clutch 9 includes a plurality of friction disks 10 nonrotatable relative to the side gear 2, and a plurality of friction disks 20 nonrotatable relative to the inner surface of the differential case 1. The friction disks 10 and the friction disks 20 are arranged in alternate relation. As shown in FIG. 6, each friction disk 10 has internal splines 11 which engage external splines 17 on a cylindrical portion 16 of the side gear 2. As shown in FIG. 7, each friction disk 20 includes a plurality of projections 21 (arranged circumferentially in a 90.degree. spaced relation) on its outer periphery. These projections 21 are in engagement with grooves 18 on the inner surface of the differential case 1 (see left-hand clutch in FIG. 4). That is, the friction disks 10 and the friction disks 20 are axially slidable (or movable to the right and left in FIG. 4), and are rotatable with the side gears 2, 2 or the differential case 1. A friction surface 12 of each of the friction disks 10 is in pressure contact with a friction surface 22 of the adjacent friction disk 20 under the influence of the pre-load springs 7, 8. As a result, the side gears 2, 2 are subject to frictional resistance by virtue of the multi-plate clutches 9, 9 and differential action is thereby limited.
A wide variety of means have been proposed to vary friction torque, all of which are designed to vary the force necessary to press the friction disks. This force will be 1000 2000 kg. Hydraulic pressure is utilized to produce and vary such large force. However, there is a disadvantage to this hydraulic system in terms of sealing. Further, it requires a large and complicated arrangement.